Soap-like material found in clay cylinders during the excavation of ancient Babylon is evidence that soap making was known as early as 2800 B.C. Inscriptions on the cylinders teach us that the contents had been made by boiling fats with ashes—a method of making soap. Later on, particularly in the 19th Century, it became common to add fragrances to soap to mask the natural smell of some of the fats used, particularly if these were animal fats, and for other aesthetic reasons.
The personal cleansing compositions used today may still include natural soaps, such as those described above, as well as synthetic soaps, which were developed during the First World War. Such cleansing compositions may take a number of forms including liquid soaps, soap bars, shampoos and body washes. The overwhelming majority of these compositions now comprise some kind of fragrance—indeed, nowadays, the fragrance is one of the key parameters driving consumer acceptance of these products.
A difficulty encountered with fragranced personal cleansing compositions is that the fragrance oils are solubilized within the surfactant micelles such that they either remain micellised or enter the continuous aqueous phase. Either way, the result is that they are typically rinsed away during the washing process rather than being deposited onto the skin as intended.
Previous researchers have employed a number of methods to counter this effect. One approach discussed in EP 0 554 024 has been to reduce solubilization of the perfume oil in the surfactant phase by adding an oil phase in which the perfume oils may reside. As a result of the oil's natural hydrophobicity, that oil phase, including the perfume oil, may deposit relatively well onto skin. A similar approach is discussed in WO 03/015736, which relates to the dissolution of the perfumes in a water-immiscible silicone phase. Again, the naturally hydrophobic silicone phase may lead to improved deposition of the fragrance oil onto skin. These approaches involve the inclusion of an additional material to the formulation to enhance fragrance delivery. That additional material may, however, have negative implications for the overall performance of the formulation, such as the lather profile.
An alternative approach discussed in WO 97/48374, WO 97/48375 and WO 97/48378, has been to form coacervates between anionic surfactant and cationic polymers, which coacervates are allegedly capable of entrapping the perfume, depositing on the skin and thus enhancing perfume deposition. The benefit of this approach is, however, limited by the nature of the surfactant and the cationic polymer, because only a few surfactant-polymer combinations will actually form coacervates, and the surfactants and polymers concerned may not be particularly suitable for personal cleansing applications (they do not necessarily give good lathering and are not necessarily mild enough).
A further alternative discussed in US 2003/166497, US 2003/166498 and US 2003/166499 has been to design the perfume/surfactant system such that, on dilution, micelles are designed to disappear due to their high Critical Micelle Concentration (CMC), and deliver fragrance bloom. After blooming from the micelles, the perfume materials enter the water continuous phase and may be washed away during rinsing. Once again, the surfactant phase is essentially a micellar phase. As discussed hereinbelow, it is believed that perfume does not deposit sufficiently well via a micellar phase.
It would be desirable to design fragranced personal cleansing products having improved perfume deposition on skin. Furthermore, it would be desirable to achieve that without adding new materials to the composition which might have negative implications for other aspects of the products' performance.